<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <template>
        <strong>{{msg}}</strong>
    </template>
</body>
<script>
    window.onload = function (){
        var temp = document.querySelector("template");
        var strongNode = temp.content.querySelector("strong")
        strongNode.innerHTML = "xxx"

        document.body.appendChild(temp.content)
    }
</script>
</html>